Engine control apparatus

ABSTRACT

An engine control apparatus is applied to a system including rotating electrical machine, a battery connected to the rotating electrical machine via a power conversion circuit, and an electric load. The engine control apparatus determines that engine speed is within a predetermined rotation speed range including at least a resonance range of an engine during a rotation drop period while engine speed drops to zero after engine combustion is stopped, and, in the case where it is determined that engine speed is within predetermined rotation speed range, selectively performs one of first rotation drop processing of increasing reduction rate of engine speed by regenerative power generation of the rotating electrical machine and second rotation drop processing of increasing reduction rate of engine speed by causing rotating electrical machine to perform power driving on an inverse rotation side. At a rotation drop control unit the first rotation drop processing is performed.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims the benefit of priorityfrom earlier Japanese Patent Application No. 2016-094755 filed on May10, 2016, the description of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an engine control apparatus.

BACKGROUND ART

In a vehicle, when an engine is started or stopped, there is a casewhere vibration may occur due to fluctuation of engine speed, and thevibration may provide a feeling of discomfort to a driver. As one of thetypes of vibration which may provide this feeling of discomfort, thereis resonance of the engine. This occurs by an excitation frequencycorresponding to engine speed being excited by matching with a resonancefrequency of a power plant such as an engine body and an automatictransmission.

For example, in a technique disclosed in PTL 1, in a hybrid carincluding a motor generator which is capable of executing power drivingand power generation, when an engine is stopped, counter torque isapplied to an engine output shaft by the motor generator at apredetermined deceleration rate. By this means, a time period whilevibration occurs is shortened by the engine speed being forcibly loweredfrom a resonance range, so that overall vibration is reduced.

CITATION LIST Patent Literature

[PTL 1] JP 2001-207885 A

SUMMARY OF THE INVENTION

Further, in recent years, in accordance with spread of idling stopcontrol, not only a hybrid car, but also a vehicle including a motorgenerator increases. Here, in the aspect of traveling performance, fueleconomy, or the like, of a vehicle, it is desirable that each functionof power driving and power generation of the motor generator is utilizedin accordance with a driving state. Concerning this point, it can beconsidered that the technique for reducing vibration using the motorgenerator disclosed in PTL 1 still has room for improvement.

The present disclosure is mainly directed to providing an engine controlapparatus which is capable of suppressing vibration in association witha resonance range of an engine using a drive scheme of rotatingelectrical machine, which is appropriate for a driving state.

A first disclosure is an engine control apparatus which is applied to asystem including rotating electrical machine which is drive-coupled toan engine output shaft and which has each function of power generationand power driving, a battery connected to the rotating electricalmachine via a power conversion circuit, and an electric load driven bypower supply from the battery, the engine control apparatus including aresonance range determining unit configured to determine that the enginespeed is within a predetermined rotation speed range including at leasta resonance range of an engine during a rotation drop period while theengine speed drops to zero after combustion of the engine is stopped,and a rotation drop control unit configured to selectively perform oneof first rotation drop processing of increasing drop speed of the enginespeed by regenerative power generation of the rotating electricalmachine and second rotation drop processing of increasing the rate ofreduction of the engine speed by causing the rotating electrical machineto perform power driving on an inverse rotation side in the case whereit is determined that the engine speed is within the predeterminedrotation speed range, and the rotation drop control unit performing thefirst rotation drop processing in the case where power consumption ofthe electric load is equal to or greater than a predetermined value.

By applying counter torque in the predetermined rotation speed rangeincluding the resonance range using the rotating electrical machinehaving each function of power driving and power generation, it ispossible to shorten a time period while the engine speed passes throughthe resonance range. Further, counter torque is greater in power drivingthan in regenerative power generation, and regenerative power generationexcels in fuel consumption compared to power driving. Therefore, bymaking it possible to select these, it is possible to suppress vibrationin association with the resonance range of the engine using the drivescheme of the rotating electrical machine which is appropriate for adriving state while taking advantages of the respective functions. Here,in circumstances where power consumption of the battery by the electricload is large, because the battery is under a heavy load, the rate ofreduction is increased by regenerative power generation. By this means,it is possible to suppress vibration while maintaining a stable powersupply state of the battery.

In a second disclosure, the rotation drop control unit performs thesecond rotation drop processing in the case where remaining capacity ofthe battery is equal to or greater than a predetermined value.

In the case where there is large remaining capacity of the battery,there is a concern that the battery may be overcharged by the rotatingelectrical machine being caused to perform regenerative powergeneration. Concerning this point, according to the above-describedconfiguration, by counter torque being applied through power driving insuch a case, it is possible to suppress vibration occurring due to theresonance range without damaging the battery.

In a third disclosure, the rotation drop control unit increases countertorque of the rotating electrical machine as the remaining capacity islarger in the case where the remaining capacity of the battery is equalto or greater than a predetermined value.

It is possible to adjust the counter torque to increase drop speed bypower driving in accordance with the remaining capacity of the battery.By this means, it is possible to shorten a time period while the enginespeed passes through the resonance range, so that a vibrationsuppression effect is improved.

A fourth disclosure is an engine control apparatus including a demandtorque calculating unit configured to calculate a demand torque demandedas counter torque of the rotating electrical machine, and the rotationdrop control unit performs the second rotation drop processing in thecase where the demand torque calculated at the demand torque calculatingunit is equal to or greater than a predetermined value.

By selecting power driving in the case where the demand torque is large,it is possible to sufficiently perform drop processing in accordancewith a demanded amount. By this means, it is possible to suppressvibration in association with the resonance range of the engine using adrive scheme which is appropriate for a driving state.

In a fifth disclosure, in addition to the rotating electrical machine,auxiliary equipment is drive-coupled to the engine output shaft, and therotation drop control unit performs the first rotation drop processingin the case where load equal to or greater than predetermined load actson the engine output shaft by operation of the auxiliary equipment.

In the case where the load equal to or greater than the predeterminedload acts on the engine output shaft by operation of the auxiliaryequipment, the engine output shaft is put into a state in which acertain amount of counter torque has been already applied. In theabove-described configuration, in such a case, drop speed is increasedby regenerative power generation. By this means, it is possible to applylarge counter torque as a whole while considering fuel economy.

In a sixth disclosure, in the case where a brake pedal is depressed, therotation drop control unit performs the first rotation drop processingassuming that power consumption of the electric load is equal to orgreater than a predetermined value.

In a state where the brake pedal is depressed, because a brake lamp islit, power consumption of the battery increases. In the above-describedconfiguration, in a state where the brake pedal is depressed, drop speedis increased by regenerative power generation assuming that powerconsumption of the electric load is equal to or greater than thepredetermined value. By this means, it is possible to suppress vibrationwhile reducing load on the battery.

In a seventh disclosure, in the case where power consumption of theelectric load is less than a predetermined value, the rotation dropcontrol unit performs the second rotation drop processing.

In the above-described configuration, in circumstances where powerconsumption by the electric load is small, the rate of reduction isincreased by power driving. Because counter torque is greater in powerdriving than in regenerative power generation, it is possible to makethe engine speed pass through the resonance range in a shorter period oftime. By this means, it is possible to effectively suppress vibration inassociation with the resonance range.

An eighth disclosure is an engine control apparatus which is applied toa system including rotating electrical machine which is drive-coupled toan engine output shaft and which has functions of both power generationand power driving, a battery connected to the rotating electricalmachine via a power conversion circuit, and an electric load driven bypower supply from the battery, the engine control apparatus including aresonance range determining unit configured to determine that enginespeed is within a predetermined rotation speed range including at leasta resonance range of an engine during a rotation drop period while theengine speed drops to zero after combustion of the engine is stopped,and a rotation drop control unit configured to selectively perform oneof first rotation drop processing of increasing drop speed of the enginespeed by regenerative power generation of the rotating electricalmachine and second rotation drop processing of increasing the rate ofreduction of the engine speed by causing the rotating electrical machineto perform power driving on an inverse rotation side, in the case whereit is determined that the engine speed is within the predeterminedrotation speed range, and the rotation drop control unit performing thesecond rotation drop processing in the case where power consumption ofthe electric load is less than a predetermined value.

In the above-described configuration, rotation drop processing isperformed by selectively using each function of power driving andregenerative power generation of the rotating electrical machine, and,in circumstances where power consumption by the electric load is small,the rate of reduction is increased by power driving. Because countertorque is greater in power driving than in regenerative powergeneration, it is possible to make the engine speed pass through theresonance range in a shorter period of time. By this means, it ispossible to effectively suppress vibration in association with theresonance range.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become clearer from the following detailed descriptionwith reference to the accompanying drawings, in which

FIG. 1 is a schematic configuration diagram of an engine control system;

FIG. 2 is a transition chart of engine speed in a rotation drop period;

FIG. 3 is a flowchart illustrating processing of stopping engine speed;

FIG. 4 is a flowchart of processing of setting counter torque;

FIG. 5 is a flowchart of crank angle stop processing;

FIG. 6 is a timing chart illustrating aspect of the processing ofstopping engine speed;

FIG. 7 is a timing chart illustrating aspect of the crank angle stopprocessing; and

FIG. 8 is a timing chart illustrating aspect of the crank angle stopprocessing.

DESCRIPTION OF EMBODIMENT

An embodiment of the present disclosure will be described below on thebasis of the drawings. In the present embodiment, a control system foran engine mounted on a vehicle is embodied. In the control system, anoperation state, or the like, of an engine is controlled mainly with anelectronic control unit (hereinafter, referred to as an ECU). An entireschematic diagram of the present system is illustrated in FIG. 1.

At a vehicle 10 illustrated in FIG. 1, an engine 11 is a four-strokeengine which is driven through combustion of a fuel such as gasoline,and which repeatedly performs respective types of process of intake,compression, expansion and exhaust. The engine 11 has four cylinders 12,and a piston 13 is held in each cylinder 12. Further, the engine 11includes a fuel injection valve (not illustrated), an ignition device(not illustrated), or the like, as appropriate. Note that, while, in thepresent embodiment, an engine with four cylinders is illustrated, theengine may have any number of cylinders. Further, the engine 11 is notlimited to a gasoline engine, and may be a diesel engine.

To the cylinder 12, air is supplied from an intake part 20. The intakepart 20 includes an intake manifold 21, and a throttle valve 22 whichadjusts an amount of air intake is provided upstream of the intakemanifold 21.

In the engine 11, an MG (motor generator) 30 is integrally provided. TheMG 30 is rotating electrical machine which is driven as an electricmotor and a generator. A crank shaft (engine output shaft) 14 of theengine 11 is mechanically connected to a crank pulley 15, and a rotatingshaft 31 of the MG 30 is mechanically connected to an MG pulley 32.Then, the crank pulley 15 is drive-coupled to the MG pulley 32 with abelt 33. Upon engine start, initial rotation (cranking rotation) isgiven to the engine 11 by rotation of the MG 30. Note that, it is alsopossible to employ a configuration where a starter motor is separatelyprovided, and initial rotation is given to the engine 11 by rotation ofthe starter motor.

Further, the MG 30 is connected to a battery 35 via an inverter 34 whichis a power conversion circuit. In the case where the MG 30 is driven asan electric motor, power is supplied to the MG 30 from the battery 35via the inverter 34 by a command from the ECU 50. As a result, the MG 30is driven. At the inverter 34, another ECU which controls the powerconversion circuit of the inverter 34 in response to a command from theECU 50 may be provided. Meanwhile, in the case where the MG 30 functionsas a generator, after power generated at the MG 30 is converted from ACto DC at the inverter 34, the battery 35 is charged with the power. Notethat electric loads 36 such as lamps and an audio device are connectedto the battery 35.

In the vehicle 10, as auxiliary devices which are driven by rotation ofthe crank shaft 14, other than the MG 30, auxiliary equipment 16 such asa water pump, a fuel pump and a compressor of an air conditioner aremounted. Note that the auxiliary device includes a device whose coupledstate with the crank shaft 14 is intermitted by clutch means, other thana device such as the auxiliary equipment 16 which is drive-coupled tothe engine 11 with a belt, or the like.

The ECU 50, which is an electronic control apparatus including amicrocomputer, or the like, configured with well-known CPU, ROM, RAM, orthe like, performs various kinds of engine control such as openingcontrol of the throttle valve 22 and control of fuel injection by thefuel injection valve on the basis of detection results of various kindsof sensors provided in the present system.

For details of sensors, to the ECU 50, a crank angle sensor 51 whichdetects a rotational position of the crank shaft 14 and engine speed Ne,an accelerator sensor 52 which detects an operation amount of anaccelerator (accelerator opening), a vehicle speed sensor 53 whichdetects vehicle speed, a brake sensor 54 which detects an operationamount of a brake pedal, an in-cylinder pressure sensor 55 which detectsan in-cylinder pressure within a cylinder, and a battery sensor 56 whichdetects a battery state of the battery 35 are connected, and signalsfrom these sensors are sequentially input to the ECU 50.

Examples of the crank angle sensor 51 can include electromagnetic pickuptype rotational position detecting means, or the like, which outputs arectangular detection signal (crank pulse signal) for each predeterminedcrank angle (for example, with a period of 10° CA). The engine speed Neis calculated from a time period taken every time the crank shaft 14rotates by 10° CA. Further, from the detection result of the rotationalposition, as well as the rotational position of the crank shaft 14 withrespect to a predetermined reference position (for example, acompression top dead center) being calculated, process of the engine 11is discerned.

The battery sensor 56 detects a voltage between terminals, acharge/discharge current, or the like, of the battery 35. On the basisof these detection values, remaining capacity (SOC) of the battery 35 iscalculated.

Further, the ECU 50 performs idling stop control of the engine 11. Inthe idling stop control, generally, combustion of the engine 11 isstopped when predetermined automatic stop conditions are fulfilled, and,thereafter, the engine 11 is restarted when predetermined restartconditions are fulfilled. In this case, the automatic stop conditionsinclude, for example, a condition that vehicle speed of the own vehicleis within an engine automatic stop speed range (for example, vehiclespeed≤10 km/h) and accelerator operation is cancelled or brake operationis performed. Further, the restart conditions include, for example, acondition that accelerator operation is started, and a condition thatbrake operation is cancelled. Note that it is also possible to employ aconfiguration where an engine control function and an idling stopfunction are implemented at different ECUs 50.

Here, at the vehicle 10, if the automatic stop conditions of the engine11 are fulfilled from an idle state, combustion of the engine 11 isstopped. Thereafter, the engine speed Ne gradually decreases and becomeszero. FIG. 2 illustrates transition of the engine speed Ne in a rotationdrop period until the engine speed Ne becomes zero after combustion ofthe engine 11 is stopped. In accordance with decrease in the enginespeed Ne, the engine speed Ne passes through the self-recovery rotationspeed, the resonance range of the engine, and predetermined rotationspeed set in advance (for example, approximately 200 rpm). Here, theself-recovery rotation speed is a lower limit of rotation speed at whichthe engine can be restarted by supply of a fuel being resumed withoutcranking being performed while combustion of the engine 11 is stopped,and is, for example, set at approximately 500 rpm.

The resonance range of the engine refers to a range of the engine speedin which resonance occurs, and is, for example, set at 300 to 400 rpm.Here, resonance is a phenomenon that an excitation frequencycorresponding to the engine speed is excited by matching with aresonance frequency of a power plant such as the engine body and anautomatic transmission. By this phenomenon, vibration increases in theresonance range of the engine. In this manner, vibration in theresonance range is one factor of unpleasant vibration occurring when theengine is stopped.

Note that the resonance range of the engine is lower than an idlerotation speed and on a higher rotation side than cranking rotationspeed of a conventional starter so as to minimize vibration occurring byresonance. Therefore, the engine speed Ne passes through the resonancerange during the rotation drop period until the engine speed Ne reacheszero after combustion of the engine is stopped.

Meanwhile, also immediately before rotation of the engine is stopped,vibration occurs by swing-back (inverse rotation) of the engine. Thisvibration occurs by a piston being pushed back in a direction of abottom dead center by compression reactive force within the cylinderwhen the engine is stopped. Note that vibration occurring in theresonance range negatively affects vibration of inverse rotation.

The present embodiment describes engine control during a rotation dropperiod until the engine speed Ne becomes zero after combustion of theengine 11 is stopped. Here, the rotation drop period is divided intothree periods on the basis of the engine speed Ne. That is, a periodfrom when combustion of the engine 11 is stopped until when the enginespeed Ne reaches an upper limit of a predetermined rotation speed rangeincluding the resonance range (specifically, a boundary value A on ahigher rotation side of the resonance range) is set as a first period, aperiod during which the engine speed Ne is within the predeterminedrotation speed range is set as a second period, and a period from whenthe engine speed Ne passes through a lower limit of the predeterminedrotation speed range (specifically, a boundary value B on a lowerrotation side of the resonance range) until when the engine speed Nebecomes zero is set as a third period. In the present embodiment, enginecontrol is performed in accordance with respective periods.

In the first period, when the automatic stop conditions are fulfilled,and combustion of the engine 11 is stopped, an opening of the throttlevalve 22 is made larger than that in the idle rotating state. By thismeans, an amount of air required to restart the engine is secured.

In the second period, rotation drop processing of increasing drop speedof the engine speed Ne in the predetermined rotation speed rangeincluding the resonance range is performed. By this means, it ispossible to shorten a time period during which the engine speed Nepasses through the resonance range, so that it is possible to suppressvibration occurring due to the resonance range.

Further, in the third period, torque on the inverse rotation side(counter torque) is applied to the crank shaft 14 so that the piston 13is stopped at a crank rotational position in a first half of expansionprocess when rotation of the crank shaft 14 is stopped. By this means,inverse rotation of the engine is suppressed, so that it is possible tosuppress vibration occurring due to the inverse rotation of the engine.

FIG. 3 is a flowchart illustrating processing procedure concerningengine control, and the present processing is repeatedly executed with apredetermined period (for example, 10 ms) by the ECU 50.

First, flags will be described. A first flag, a second flag and a thirdflag in the drawing respectively correspond to the above-described firstperiod, second period and third period, and indicate whether the enginespeed Ne is within each period. Each flag indicates that the enginespeed Ne is within the period in a case of 1, and indicates that theengine speed Ne does not fall within the period in a case of 0. Notethat all the flags are set at 0 in initial setting.

In step S11, it is determined whether the third flag is 1. In step S12,it is determined whether the second flag is 1. In step S13, it isdetermined whether the first flag is 1. In the case where negativedetermination results are obtained in all of step S11 to step S13 in aninitial state, the processing proceeds to step S14, and it is determinedwhether the engine automatic stop conditions are fulfilled. Then, in thecase where a negative determination result is obtained in step S14, thepresent processing is finished without any processing being performed.

Meanwhile, in the case where it is determined in step S14 that theengine automatic stop conditions are fulfilled, the processing proceedsto step S15, and the first flag is set at 1. In the following step S16,combustion of the engine 11 is stopped, and the processing proceeds tostep S17. In step S17, the opening of the throttle valve 22 is madelarger than the opening in the idle rotating state (specifically, theopening is made larger than the opening in the idle rotating state byequal to or greater than 10%, and is, for example, made full opening),and the present processing is finished.

In this manner, control is performed so that the opening of the throttlevalve 22 is made larger than the opening in the idle rotating state whencombustion of the engine 11 is stopped. Note that the processing in stepS17 corresponds to a throttle control unit.

Meanwhile, in the case where it is determined in step S13 that the firstflag is 1, the processing proceeds to step S18, and it is determinedwhether the engine speed Ne is equal to or less than predeterminedrotation speed Ne1 which is an upper limit of the predetermined rotationspeed range. Note that, in the present embodiment, the boundary value Aon the higher rotation side of the resonance range is set as thepredetermined rotation speed Ne1. That is, in step S18, it is determinedwhether the engine speed Ne reaches the boundary value A on the higherrotation side of the resonance range.

In the case where it is determined in step S18 that the engine speed Neis greater than the predetermined rotation speed Ne1, the presentprocessing is finished without any processing being performed.Meanwhile, in the case where it is determined in step S18 that theengine speed Ne is equal to or less than the predetermined rotationspeed Ne1, that is, in the case where the engine speed Ne transitions tothe resonance range, the processing proceeds to step S19, and the secondflag is set at 1, and the first flag is reset to 0.

If the engine speed Ne transitions to the resonance range, processing ofincreasing the rate of reduction of the engine speed Ne is executed. Asthe processing of increasing the rate of reduction, in the presentembodiment, counter torque is applied using the MG 30 which is anauxiliary device. Then, in step S20, first, the counter torque is set.

The MG 30 has a power generation function as a generator and a powerdriving function as an electric motor, and application of counter torqueis executed using the respective functions. Here, counter torque isgreater in power driving than in regenerative power generation, andregenerative power generation excels in fuel consumption compared topower driving. Therefore, it is preferable to use each function inaccordance with an operation state. In such a case, which function isused is judged on the basis of various parameters. In the presentembodiment, regenerative power generation or power driving of the MG 30is selected in accordance with power consumption of the electric load 36connected to the battery 35, a state of remaining capacity of thebattery 35, demand torque required for application of counter torque,and a load by operation of the auxiliary equipment 16. Further, in thiscase, in the case where power consumption of the electric load 36 islarge, or in the case where the load of the auxiliary equipment 16 islarge, regenerative power generation is selected, and, in the case wherethe remaining capacity of the battery 35 is large, or in the case wherethe demand torque of the counter torque is large, power driving isselected.

FIG. 4 illustrates a flowchart of setting of the counter torque. First,in step S31, it is determined whether the power consumption of theelectric load 36 is equal to or greater than a predetermined value. Forexample, examples of the electric load 36 can include, lamps, anelectric pump, or the like. More specifically, it is determined whethera brake pedal is depressed. Because a brake lamp is lighted in a statewhere the brake pedal is depressed, power consumption becomes large. Inthe case where it is determined in step S31 that the brake pedal isdepressed, the processing proceeds to step S32, and it is determined toapply counter torque through regenerative power generation. In thiscase, because power consumed by the electric load 36 is large, byutilizing regenerative power generation, it is possible to suppressvibration while reducing a burden on the battery 35.

Meanwhile, in the case where a negative determination result is obtainedin step S31, the processing proceeds to step S33, and a function isselected in accordance with the remaining capacity of the battery 35.Here, for example, it is determined whether the SOC of the battery 35 isequal to or greater than a threshold Th1. In the case where it isdetermined in step S33 that the SOC is equal to or greater than thethreshold Th1, the processing proceeds to step S36, and it is determinedto apply counter torque through power driving. Note that a value of thethreshold Th1 may be changed as appropriate, and, for example, may be avalue from which it can be judged that the battery 35 is in a fullycharged state in the case where the SOC is equal to or greater than thethreshold Th1.

Here, in calculation of the SOC, an estimation method based on an opencircuit voltage (OCV) and a calculation method through currentintegration are used. Here, an open circuit voltage of the battery 35 isacquired, the SOC is estimated using the acquired value and mapindicating correspondence relationship between the open circuit voltageand the SOC, a charge/discharge current flowing through the battery 35is acquired, and the SOC is calculated by performing calculationprocessing on the acquired value. Note that, in the case where countertorque is applied through power driving, greater counter torque may beset as the remaining capacity is greater. In this case, because it ispossible to further shorten a time period during which the engine speedNe passes through the resonance range, it can be considered that aneffect of suppressing vibration is improved.

Meanwhile, in the case where a negative determination result is obtainedin step S33, the processing proceeds to step S34, and a function isselected in accordance with the demand torque of the counter torque. Forexample, it is determined whether the demand torque is equal to orgreater than a threshold Th2. In the case where it is determined in stepS34 that the demand torque is equal to or greater than the thresholdTh2, the processing proceeds to step S36, and it is determined to applycounter torque through power driving.

Further, in the case where a negative determination result is obtainedin step S34, the processing proceeds to step S35, and a function isselected in accordance with the load of the auxiliary equipment 16. Forexample, it is determined whether the load by operation of the auxiliaryequipment 16 is equal to or greater than a threshold Th3. In the casewhere it is determined in step S35 that the load is equal to or greaterthan the threshold Th3, the processing proceeds to step S32, and it isdetermined to apply counter torque through regenerative powergeneration. Note that, while, in such a case, power consumption of theelectric load 36 is less than a predetermined value (step S31: No),regenerative power generation is selected in view of other parametersindicating an operation state of the vehicle.

Meanwhile, in the case where a negative determination result is obtainedin step S35, the processing proceeds to step S36, and it is determinedto apply counter torque through power driving. As described above, afterregenerative power generation or power driving is determined on thebasis of the parameters, the processing transitions to step S21 in FIG.3, and counter torque is applied. Note that it is also possible toemploy a configuration where, in the case where a result in step S31 isNo, the processing proceeds to step S36, and power driving is selectedwithout determination from step S33 to step S35 being performed. Thatis, it is also possible to employ a configuration where, in the casewhere the power consumption of the electric load 36 is less than thepredetermined value, counter torque is applied through power driving.

Here, application of counter torque through power driving corresponds tofirst rotation drop processing, and application of counter torquethrough regenerative power generation corresponds to second rotationdrop processing.

Then, in the case where it is determined in step S12 in FIG. 3 that thesecond flag is 1, the processing proceeds to step S22, and it isdetermined whether the engine speed Ne is less than predeterminedrotation speed Ne2 which is a lower limit of the predetermined rotationspeed range. Note that, in the present embodiment, the boundary value Bon the lower rotation side of the resonance range is set as thepredetermined rotation speed Ne2. That is, in step S22, it is determinedwhether the engine speed Ne passes through the boundary value B on thelower rotation side of the resonance range.

In the case where it is determined in step S22 that the engine speed Neis less than the predetermined rotation speed Ne2, that is, in the casewhere the engine speed Ne transitions to the third period, theprocessing proceeds to step S23, and the third flag is set at 1, and thesecond flag is reset to 0. In the following step S24, the counter torqueapplied in step S21 is stopped. Meanwhile, in the case where it isdetermined in step S22 that the engine speed Ne is equal to or greaterthan the predetermined rotation speed Ne2, the present processing isfinished without any processing being performed.

Note that the processing in step S18 and step S22 corresponds to aresonance range determining unit which determines that the engine speedpasses through the resonance range of the engine. Further, theprocessing in step S20 and step S21 corresponds to a rotation dropcontrol unit. In this manner, in the present embodiment, in the casewhere it is determined that the engine speed passes through theresonance range, counter torque is applied to the engine output shaftusing either power driving or regenerative power generation of therotating electrical machine.

Then, in the case where it is determined in step S11 that the third flagis 1, the processing proceeds to step S25, and processing of subroutineillustrated in FIG. 5 is executed. That is, when the engine speed Netransitions to the third period, crank angle stop processing forsuppressing inverse rotation of the engine is performed. Here, countertorque is applied at a predetermined timing based on the engine speed sothat the piston 13 is stopped at a position in a first half of expansionprocess, that is, the piston 13 of the next combustion cylinder isstopped at a position in a first half of compression process. Further,in the case where the piston 13 is not stopped at a desired position byapplication of counter torque, backup processing of applying torque on apositive rotation side (positive torque) to the engine output shaft isalso executed. That is, in the crank angle stop processing, control isperformed so that the piston 13 is not stopped at a position in a secondhalf of compression process, that is, the piston 13 is not stopped at aposition at which compression reactive force is generated.

In step S41 in FIG. 5, first, it is determined whether it is a timingfor applying positive torque to the engine output shaft. In this step,an affirmative determination result is obtained in the case where it isdetermined to execute backup processing, and a negative determinationresult is obtained in step S41 in initial setting. In the following stepS42, it is determined whether it is a timing for applying counter torqueto the engine output shaft. In the present embodiment, for example, inthe case where the engine speed Ne when the piston 13 is located at acompression TDC is equal to or less than predetermined rotation speedNe3, it is determined that it is a timing for applying counter torque.Here, in the case where it is determined that it is a timing forapplying counter torque, the processing proceeds to step S43, countertorque is applied to the engine output shaft, and the present processingis finished.

The predetermined rotation speed Ne3 is rotation speed at which it isdetermined that rotation of the engine output shaft is stopped until thepiston passes through a first half period of the expansion process bycounter torque being applied from a timing at which the piston islocated at the compression TDC. Note that the predetermined rotationspeed Ne3 is set as a value smaller than the predetermined rotationspeed Ne2 which is the lower limit of the predetermined rotation speedrange.

Meanwhile, in the case where it is determined in step S42 that it is nota timing for applying counter torque, the processing proceeds to stepS44, and it is determined whether counter torque is applied. Here, inthe case where a negative determination result is obtained in step S44,the present processing is finished without any processing beingperformed.

Meanwhile, in the case where it is determined in step S44 that countertorque is applied, the processing proceeds to step S45, and it isdetermined whether the crank rotational position detected by the crankangle sensor 51 is a set predetermined angle (for example, ATDC70° CA).In the case where it is determined that the rotational position is thepredetermined angle, the processing proceeds to step S46, and it isdetermined whether the engine speed Ne is equal to or less thanpredetermined rotation speed Ne4. Meanwhile, in the case where anegative determination result is obtained in step S45, the presentprocessing is finished without any processing being performed.

In the case where it is determined in step S46 that the engine speed Neis equal to or less than the predetermined rotation speed Ne4, that is,in the case where it is determined that the piston 13 is stopped at aposition in the first half of the expansion process, the processingproceeds to step S47, and an instruction of stopping the counter torqueapplied in step S43 is given. By this means, the counter torque appliedto the engine output shaft is stopped. Subsequently, the processingproceeds to step S48, the third flag is reset to 0, and the presentprocessing is finished.

Note that step S45 and step S46 correspond to a stop determining unit.The predetermined rotation speed Ne4 at the predetermined angle can berespectively arbitrarily changed, and only has to be a value from whichit can be determined whether the piston 13 is actually stopped at thecrank rotational position up to the first half of the expansion processafter the counter torque is applied in step S43.

Meanwhile, in the case where it is determined in step S46 that theengine speed Ne is greater than the predetermined rotation speed Ne4,that is, in the case where it is determined that the piston 13 is notstopped at the position in the first half of the expansion process, theprocessing proceeds to step S49, and an instruction for allowing thepiston 13 to get over the next compression TDC is given. That is, it isjudged to execute backup processing. Then, in the present embodiment, inthe case where this processing is executed, and the crank rotationalposition is located at the predetermined rotation angle (for example,ATDC90° CA), it is determined that it is a timing for applying positivetorque to the engine output shaft (step S41: Yes).

If an affirmative determination result is obtained in step S41, theprocessing proceeds to step S50, positive torque is applied, and thepresent processing is finished. Thereafter, the processing proceeds tostep S42 again, and the crank angle stop processing is executed untilthe third flag is finally reset to 0.

Engine control in the rotation drop period until the engine speed Necompletely becomes zero after combustion of the engine 11 is stoppedwill be described next using a timing chart in FIG. 6.

First, if the automatic stop conditions are fulfilled at a timing t11from the idle state, the first flag is set at 1. At this time, theopening of the throttle valve 22 is controlled to be larger than theopening in the idle state. Thereafter, if the engine speed Ne becomesequal to or less than the predetermined rotation speed Ne1 at a timingt12, at the same time as the second flag being set at 1, the first flagis reset to 0. At this time, counter torque is applied to the engineoutput shaft as rotation drop processing. Then, if the engine speed Neis below the predetermined rotation speed Ne2 at a timing t13, at thesame time as the third flag being set at 1, the second flag is reset to0. At this time, the rotation drop processing is stopped, and in thefollowing third period, the crank angle stop processing is executed.Then, the engine speed Ne becomes zero at a timing t14.

Subsequently, the crank angle stop processing in the case where theengine speed Ne is within the third period will be described usingtiming charts in FIG. 7 and FIG. 8. These respectively illustrate casesof different determination results in step S46 in FIG. 5 after countertorque is applied. FIG. 7 illustrates a case where an affirmativedetermination result is obtained in step S46, and only counter torque isapplied in the third period, while FIG. 8 illustrates a case where anegative determination result is obtained in step S46, and, in additionto counter torque, positive torque is also applied in the third period.Note that these drawings illustrate change of an in-cylinder pressure ofeach cylinder. The in-cylinder pressure increases as the piston 13 comescloser to the compression TDC, and becomes a maximum at the compressionTDC. Further, a local maximum value of the in-cylinder pressuredecreases as the engine speed Ne decreases. Note that firing order ofthe respective cylinders is #1, #2, #3 and #4 for the purpose ofillustration.

In FIG. 7, while the engine speed Ne drops, when the engine speed Nebecomes equal to or less than Ne3 at a timing t21 (at a timing at whicha first cylinder (#1) reaches the compression TDC), counter torque isapplied to the engine output shaft, which leads to increase in dropspeed of the engine speed Ne, and the engine speed Ne approaches zero.Then, when the engine speed Ne at a timing t22 (at a timing at which thefirst cylinder (#1) reaches a predetermined crank angle position (forexample, ATDC70° CA)) becomes equal to or less than the predeterminedrotation speed Ne4, application of the counter torque is stopped.Thereafter, rotation of the engine 11 is stopped at a timing t23. Atthis time, the piston 13 of the first cylinder (#1) is stopped at aposition in the first half of the expansion process (for example,ATDC80° CA).

In FIG. 8, when the engine speed Ne becomes equal to or less than Ne3 ata timing t31 (at a timing at which the first cylinder (#1) reaches thecompression TDC), counter torque is applied. Then, when the engine speedNe at a timing t32 (at a timing at which the first cylinder (#1) reachesa predetermined crank angle position (for example, ATDC70° CA)) isgreater than the predetermined rotation speed Ne4, backup processing isexecuted. That is, at a timing t33, positive torque is applied so thatthe second cylinder (#2) can get over the next compression TDC. Here,the timing t33 is set at a timing at which the first cylinder (#1) islocated at a predetermined crank angle position (for example, ATDC90°CA).

Then, when the engine speed Ne becomes equal to or less than thepredetermined rotation speed Ne3 again at a timing t34 at which thesecond cylinder (#2) reaches the compression TDC, counter torque isapplied again. Thereafter, when the engine speed Ne at a timing t35 (ata timing at which the second cylinder (#2) reaches a predetermined crankangle position (for example, ATDC70° CA)) becomes equal to or less thanthe predetermined rotation speed Ne4, application of the counter torqueis stopped. Then, rotation of the engine 11 is stopped at a timing t36,and at that time, the second cylinder (#2) is stopped at a position inthe first half of the expansion process (for example, ATDC80° CA).

In the present embodiment, a four-cylinder engine is described as amulti-cylinder engine. In such a case, when the piston 13 in onecylinder is stopped at a position in the first half period of theexpansion process, the pistons 13 in other cylinders are not stopped ata position in the second half period of the compression process, thatis, at a position at which compression reactive force is generated.

According to the present embodiment described in detail above, it ispossible to obtain the following excellent effects.

In a vehicle having an idling stop function, when combustion of theengine 11 is stopped, by making the opening of the throttle valve 22larger than the opening in the idle rotating state, it is possible tosecure a sufficient amount of air required upon restart of the engine.Further, by applying counter torque using the MG 30 so that drop speedof the engine speed is increased in the resonance range, it is possibleto shorten a time period during which the engine speed passes throughthe resonance range. In this case, while there is concern that vibrationis increased in the resonance range in a state where the throttleopening is large, by shortening the time period during which the enginespeed passes through the resonance range, it is possible to suppressincrease in vibration. By this means, in a vehicle having an idling stopfunction, it is possible to secure startability upon restart whilesuppressing occurrence of vibration when the engine is automaticallystopped.

A configuration is employed where the opening of the throttle valve 22is made larger than the opening in the idle rotating state at a timepoint at which combustion of the engine 11 is stopped. By this means,even in the case where restart conditions are fulfilled immediatelyafter combustion is stopped, it is possible to secure a sufficientamount of air, so that startability upon restart becomes favorable.

A configuration is employed where, in the resonance range, countertorque is applied using the MG 30. In this case, it is possible to applygreater counter torque to the engine output shaft compared to torqueapplied using the auxiliary equipment 16. Therefore, a time periodduring which the engine speed passes through the resonance range isfurther shortened, so that an effect of suppressing vibration isimproved.

Further, a configuration is employed where, in application of countertorque using the MG 30, regenerative power generation or power drivingcan be selected. Here, counter torque is greater in power driving thanin regenerative power generation, and regenerative power generationexcels in fuel consumption compared to power driving. By this means, itis possible to select a drive system while obtaining respectiveadvantages of regenerative power generation and power driving inaccordance with an operation state.

A configuration is employed where, concerning selection of the drivesystem of the MG 30, regenerative power generation or power driving canbe selected in accordance with power consumption of the electric load 36connected to the battery 35. In this case, in the case where powerconsumption of the electric load 36 is equal to or greater than apredetermined value, because the battery 35 is under a heavy load,counter torque is applied through regenerative power generation. By thismeans, it is possible to suppress vibration while maintaining a stablepower state of the battery 35.

Specifically, a configuration is employed where, in a case of a statewhere a brake pedal is depressed, counter torque is applied whileregenerative power generation is selected. In a state where the brakepedal is depressed, power consumption of the battery 35 increases inassociation with lighting of a brake lamp. Therefore, it is possible tosuppress vibration while maintaining a stable power state of the battery35.

Concerning selection of the drive system of the MG 30, further, aconfiguration is employed where regenerative power generation or powerdriving can be selected on the basis of the remaining capacity of thebattery 35. In this case, in the case where the remaining capacity isequal to or greater than the threshold Th1, counter torque is appliedthrough power driving. In the case where there is large remainingcapacity of the battery 35, there is a concern that the battery 35 isovercharged by the rotating electrical machine being caused to performregenerative power generation. Concerning this point, by counter torquebeing applied through power driving, it is possible to suppressvibration occurring due to the resonance range without damaging thebattery 35.

In the case where it is determined that the cylinder is located at acompression top dead center immediately before the engine speed becomeszero in the third period, counter torque is applied from the compressiontop dead center using the MG 30. In this case, by applying countertorque, it is possible to stop the piston 13 at a position in the firsthalf of the expansion process. By this means, by suppressing occurrenceof inverse rotation of the engine, it is possible to reduce vibration inassociation with the inverse rotation of the engine.

Specifically, it is determined that the cylinder is located at the lastcompression top dead center on the basis that the engine speed at thecompression top dead center of the engine 11 is equal to or less than apredetermined value. Here, the predetermined value is a value from whichit is determined that the piston 13 is stopped at the position in thefirst half of the expansion process by application of the countertorque. Therefore, it is possible to stop the piston 13 at a desiredposition, so that it is possible to reduce vibration in association withthe inverse rotation of the engine.

Further, a configuration is employed where a stop determining unit isprovided which determines whether the piston 13 is actually stopped at adesired position after the counter torque is applied, and, in the casewhere it is determined that the piston 13 is stopped at the desiredposition, application of the counter torque is stopped. In this case,when rotation of the engine is stopped at a position in the first halfof the expansion process, application of the counter torque iscancelled. By this means, it is possible to prevent inverse rotation ofthe engine due to counter torque.

Further, backup processing is provided in stop control in the thirdperiod. That is, in the case where it is determined by the stopdetermining unit that the piston 13 is not stopped at a desiredposition, positive torque is applied once so that the piston 13 can getover the next compression TDC. Then, when the cylinder reaches thecompression TDC, processing of applying counter torque again from thatpoint, and stopping the piston at the position in the first half of theexpansion process is performed. By this means, it is possible to stopthe piston 13 at the position in the first half of the expansion processmore reliably, so that it is possible to improve an effect ofsuppressing vibration.

After combustion of the engine 11 is stopped, in the rotation dropperiod until the engine speed drops to zero, counter torque is appliedin the resonance range, and counter torque by crank stop processing orpositive/counter torque is applied in the third period, using the MG 30.By this means, it is possible to suppress also vibration related to theinverse rotation of the engine as well as vibration in the resonancerange. Further, in this case, it is possible to reduce a negative effectof vibration in the resonance range on vibration due to the inverserotation. In this manner, by combining application of counter torque inthe resonance range and processing in the third period, it is possibleto synergistically suppress vibration occurring from when combustion ofthe engine 11 is stopped until when rotation of the engine 11 isstopped.

The present disclosure is not limited to the above-described embodiment,and, for example, may be implemented as follows.

While, in the above-described embodiment, a configuration is employedwhere counter torque is applied using the MG 30 as the auxiliary device,any auxiliary device which can apply counter torque to the engine outputshaft may be used. Examples of the auxiliary device can include, forexample, the auxiliary equipment 16 such as a water pump and a fuelpump. In this case, also in a vehicle on which the MG 30 is not mounted,it is possible to apply counter torque using a device which is normallyprovided at the vehicle. Therefore, it is not necessary to separatelyprovide a new device, and is economical.

In the above-described embodiment, counter torque is applied in thesecond period assuming that the predetermined rotation speed range isthe resonance range. That is, an upper limit of the predeterminedrotation speed range is set as the boundary value A on the higherrotation side of the resonance range, and a lower limit of thepredetermined rotation speed range is set as the boundary value B on thelower rotation side of the resonance range. Concerning this point, anyconfiguration may be employed if the predetermined rotation speed rangeis set so as to include the resonance range.

For example, it is also possible to employ a configuration where thepredetermined rotation speed range is determined while setting thepredetermined rotation speed on the higher rotation side of theresonance range as the upper limit. In this case, it is determined instep S18 in FIG. 3 whether the engine speed Ne is equal to or less thanthe predetermined rotation speed Ne1 set on the higher rotation side ofthe boundary value A of the resonance range, and if a determinationresult in step S18 is Yes, application of counter torque is started.According to this configuration, after combustion of the engine 11 isstopped, by counter torque being applied before the engine speed reachesthe resonance range, it is possible to improve response to drop speed bythe counter torque near the boundary value A of the resonance range. Asa result, a time period during which the engine speed passes through theresonance range is further shortened, so that an effect of suppressingvibration is improved.

Further, it is also possible to employ a configuration where thepredetermined rotation speed range is determined while setting theself-recovery rotation speed on the higher rotation side of theresonance range as the upper limit. In this case, it is determined instep S18 in FIG. 3 whether the engine speed Ne is equal to or less thanthe predetermined rotation speed Ne1 set at the self-recovery rotationspeed, and in the case where a determination result in step S18 is Yes,application of counter torque is started. According to thisconfiguration, in a state where the engine speed exceeds thepredetermined rotation speed Ne1 which is an early stage in which theengine speed starts to drop in association with stop of combustion ofthe engine, it is possible to expect a possibility that the engine isautonomously recovered without the rate of reduction of the engine speedbeing increased. As a result, it is possible to improve response to therate of reduction in the resonance range and improve an effect ofsuppressing vibration while reducing power consumption required forrestart.

Other than the above configurations, it is also possible to employ aconfiguration where the predetermined rotation speed range is determinedwhile setting the predetermined rotation speed set in advance on thelower rotation side of the resonance range as the lower limit. In thiscase, it is determined in step S22 in FIG. 3 whether the engine speed Neis less than the predetermined rotation speed Ne2 set in advance, and inthe case where a determination result in step S22 is Yes, application ofthe counter torque is stopped. According to this configuration, it ispossible to expect a possibility that the engine is restarted bycranking without the rate of reduction of the engine speed beingincreased during a period while the engine speed is within a rangebetween the predetermined rotation speed set in advance and zero. As aresult, it is possible to secure startability of restart whilesuppressing vibration in the resonance range.

Further, it is also possible to set the predetermined rotation speedrange by combining settings of the above-described upper limit and lowerlimit of the predetermined rotation speed range. For example, it ispossible to set the upper limit of the predetermined rotation speedrange as the self-recovery rotation speed on the higher rotation side ofthe resonance range and set the lower limit as the predeterminedrotation speed set in advance on the lower rotation side of theresonance range. In such a case, it is possible to make the engine speedpromptly pass through the rotation speed range in which the enginecannot be restarted by means of fuel supply or cranking. Meanwhile, in arange in which the engine can be restarted, drop speed of the enginespeed is not increased. As a result, it is possible to securestartability of restart while suppressing vibration in the resonancerange.

While, in the above-described embodiment, a configuration is employedwhere, concerning application of counter torque in the resonance range,regenerative power generation or power driving of the MG 30 is selectedin accordance with power consumption of the electric load 36 connectedto the battery 35, the state of the remaining capacity of the battery35, the demand torque required for application of counter torque, andthe load by operation of the auxiliary equipment 16, it is also possibleto employ a configuration where regenerative power generation or powerdriving is selected in accordance with other parameters. Examples ofother parameters can include rotation speed, or the like, of the MG 30.

Note that, in selection of the drive system of the MG 30, priority maybe set on the above-described parameters. For example, determinationbased on a driving state of the electric load 36 can be used as the toppriority, and, subsequently, an order of priority can be set in order ofthe state of the remaining capacity of the battery 35, the demand torquerequired for application of counter torque, and the load by operation ofthe auxiliary equipment 16.

While, in the above-described embodiment, the SOC of the battery 35 isused as the state of the remaining capacity of the battery 35, the stateof the remaining capacity of the battery 35 is not limited to this, and,for example, a voltage between the terminals of the battery 35 may beused.

In the above-described embodiment, a configuration is employed where, inthe case where it is determined that the power consumption of theelectric load 36 is equal to or greater than a predetermined value,specifically, in the case where the brake pedal is depressed, countertorque is applied through regenerative power generation. Concerning thispoint, it is, for example, also possible to employ a configurationwhere, in the case where it is determined that the power consumption ofthe electric load 36 is less than a predetermined value, specifically,in the case where the brake pedal is not depressed, counter torque isapplied through power driving. In this case, because power consumptionby the electric load 36 is small, it is possible to suppress a totalamount of power even if power driving is performed. Further, byutilizing power driving, it is possible to make the engine speed passthrough the resonance range in a shorter time period. By this means, itis possible to effectively suppress vibration.

Concerning the backup processing in the third period, while, in FIG. 8,a configuration is employed where counter torque is applied in a periodfrom the timing t31 to the timing t33, it is also possible to employ aconfiguration where counter torque is stopped at a time point at whichstop is determined at the timing t32.

Further, in FIG. 8, a configuration is employed where positive torque isapplied in a period from the timing t33 to the timing t34 (a timing atwhich the second cylinder (#2) reaches the compression TDC). Concerningthis point, a period during which positive torque is applied is notlimited to this, and it is only necessary to employ a configurationwhere positive torque is applied so that the piston (here, the secondcylinder (#2)) can get over the compression TDC, and it is also possibleto employ a configuration where application of the positive torque isstopped before the compression TDC.

A magnitude of the counter torque applied in the crank angle stopprocessing only has to be determined in advance as torque required forstopping the piston 13 at the position in the first half of theexpansion process. Further, it is also possible to provide means forpredicting a stop position of the piston 13 every moment when rotationof the engine is stopped, and apply counter torque while performingfeedback control of adjusting torque on the basis of the predicted stopposition.

Magnitudes of the counter torque and the positive torque applied in thecrank angle stop processing may be changed as appropriate, and may bethe same or different from each other. Further, magnitudes of firstcounter torque and second counter torque in the case where backupprocessing is performed may be changed as appropriate. For example, thesecond counter torque may be set greater than the first counter torque,and according to this configuration, it can be considered that thepiston can be stopped at a desired position more reliably.

In the above-described embodiment, in the crank angle stop processing, atiming for applying counter torque is judged in accordance with whetherthe engine speed Ne at the compression TDC is below the predeterminedrotation speed Ne3. Concerning this point, the crank angle position atwhich the predetermined rotation speed Ne3 is set is not limited to thecompression TDC, and judging may be performed with the engine speed Neat other crank angle positions being set as the threshold. Note that, inthis case, it is also possible to employ a configuration whereapplication of counter torque is started from the crank angle positionat which the threshold is set.

While, in the above-described embodiment, in the crank angle stopprocessing, the predetermined rotation speed Ne3 is provided as thethreshold for the engine speed to judge a timing for applying countertorque, the judging method is not limited to this method. For example,it is also possible to use a method of judging a timing from transitionof drop of the engine speed Ne. In this case, the ECU 50, for example,calculates a rotation speed drop amount ΔNe from the engine speed Ne foreach compression TDC and estimates a compression TDC (i) at which it ispredicted that the engine speed Ne is below zero. Then, it is possibleto set at timing at which the piston 13 reaches a compression TDC (i−1)immediately before the compression TDC (i) as a timing for applyingcounter torque.

The above-described control in the rotation drop period until the enginespeed becomes zero may be performed in a case of stop by ignition switchoperation by a driver as well as in a case of automatic stop of theengine. Further, the above-described control may be also performed in acase of stop in a vehicle which does not have an idling stop function.

While the present disclosure has been described with reference to theexamples, the present disclosure is not limited to the examples andstructures. The present disclosure incorporates various modifiedexamples and modifications within an equivalent range. In addition,various combinations, forms, and other combinations and forms includingonly one element or more or less elements fall within the scope and theconceptual range of the present disclosure.

1. An engine control apparatus which is applied to a system includingrotating electrical machine which is drive-coupled to an engine outputshaft and which has functions of both power generation and powerdriving, a battery connected to the rotating electrical machine via apower conversion circuit and an electric load driven by power supplyfrom the battery, the engine control apparatus comprising: a resonancerange determining unit configured to determine that engine speed iswithin a predetermined rotation speed range including at least aresonance range of an engine during a rotation drop period while theengine speed drops to zero after combustion of the engine is stopped;and a rotation drop control unit configured to selectively perform oneof first rotation drop processing of increasing a rate of reduction ofthe engine speed by regenerative power generation of the rotatingelectrical machine and second rotation drop processing of increasing therate of reduction of the engine speed by causing the rotating electricalmachine to perform power driving on an inverse rotation side in a casewhere it is determined that the engine speed is within the predeterminedrotation speed range, wherein the rotation drop control unit performsthe first rotation drop processing in a case where power consumption ofthe electric load is equal to or greater than a predetermined value. 2.The engine control apparatus according to claim 1, wherein the rotationdrop control unit performs the second rotation drop processing in a casewhere the remaining capacity of the battery is equal to or greater thana predetermined value.
 3. The engine control apparatus according toclaim 2, wherein the rotation drop control unit increases counter torqueof the rotating electrical machine as the remaining capacity is largerin a case where the remaining capacity of the battery is equal to orgreater than the predetermined value.
 4. The engine control apparatusaccording to claim 1, further comprising: a demand torque calculatingunit configured to calculate demand torque demanded as counter torque ofthe rotating electrical machine, wherein the rotation drop control unitperforms the second rotation drop processing in a case where the demandtorque calculated at the demand torque calculating unit is equal to orgreater than a predetermined value.
 5. The engine control apparatusaccording to claim 1, wherein, in addition to the rotating electricalmachine, auxiliary equipment is drive-coupled to the engine outputshaft, and the rotation drop control unit performs the first rotationdrop processing in a case where load equal to or greater thanpredetermined load acts on the engine output shaft by operation of theauxiliary equipment.
 6. The engine control apparatus according to claim1, wherein, in a case where a brake pedal is depressed, the rotationdrop control unit performs the first rotation drop processing assumingthat power consumption of the electric load is equal to or greater thana predetermined value.
 7. The engine control apparatus according toclaim 1, wherein, in a case where power consumption of the electric loadis less than a predetermined value, the rotation drop control unitperforms the second rotation drop processing.
 8. An engine controlapparatus which is applied to a system including rotating electricalmachine which is drive-coupled to an engine output shaft and which hasfunctions of both power generation and power driving, a batteryconnected to the rotating electrical machine via a power conversioncircuit, and an electric load driven by power supply from the battery,the engine control apparatus comprising: a resonance range determiningunit configured to determine that engine speed is within a predeterminedrotation speed range including at least a resonance range of an engineduring a rotation drop period while the engine speed drops to zero aftercombustion of the engine is stopped; and a rotation drop control unitconfigured to selectively perform one of first rotation drop processingof increasing drop speed of the engine speed by regenerative powergeneration of the rotating electrical machine and second rotation dropprocessing of increasing the rate of reduction of the engine speed bycausing the rotating electrical machine to perform power driving on aninverse rotation side, in a case where it is determined that the enginespeed is within the predetermined rotation speed range, wherein therotation drop control unit performs the second rotation drop processingin a case where power consumption of the electric load is less than apredetermined value.